248 / 2024-02-28 16:22:32

Estimation of Probable Maximum Flood in Himalayan Region Based on SWAT Model

SWAT model; probable maximum precipitation; probable maximum flood; Himalayan region

In order to estimate the probable maximum flood (PMF) for the design of hydropower station in ungauged basin, the daily hydrological model and reanalysis meteorological data are used to simulate the extreme flood. The Arun River is selected as the study area, which is a tributary of the Sapt Kosi River, located between latitudes 26°56′ to 29°09′N and longitudes 85°42′ to 88°57′E. Hershfield method is used to estimate the 3-day PMP using the mean, standard deviation and the frequency factor of the annual maximum rainfall series using the observed and Climate Forecast System Reanalysis (CFSR) data of 30 stations. The 3-day estimated weighted PMPs are divided according to the ratios of the maximum historical 3-day rainfall in recorded meteorological station. The Soil and Water Assessment Tool (SWAT) model is used to simulate the PMF by using the 3-day PMP. For the calibration of the model, the daily discharge records from May 1985 to Decmber 2000, of Uwa Gaon on the Arun River are used. The calibration period was chosen to be 1985-2000 with 2 years of a warm up period. The Nash's Efficiency and relative error are used to assess the calibration performance of the SWAT model. The results show that The Nash's Efficiency (NE) estimated from the model is 78% with a relative error (RE) of 0.73 % for the calibration period from 1985 to 2000, suggesting that the model is suitable for the simulation of PMF. The maximum simulated daily discharge is 4536 m³/s at the dam site of the hydropower station. Since the average maximum instantaneous flood peak at the Uwa Gaon Station is about 1.1 times of the maximum 1-day flood, the PMF values at the dam site is estimated to be 4990 m³/s. The simulated PMF is close to the 1 in 10000 year return flood (4870 m³/s) at dam site calculated by flood frequency analysis. The recommended PMF value at dam site is 4990 m³/s for security consideration. The proposed method provide a new approach to estimate PMF using the reanalysis meteorological data by hydrological model in ungauged basin.